# Difference between "Leaf-level Mesh Part" and "A CAD Part created in 3D-CAD"?

 Register Blogs Members List Search Today's Posts Mark Forums Read

 January 23, 2014, 10:29 Difference between "Leaf-level Mesh Part" and "A CAD Part created in 3D-CAD"? #1 New Member   Join Date: Aug 2013 Posts: 14 Rep Power: 8 Hello everybody, Can someone please describe the difference between a "Leaf-level Mesh Part" and "A CAD Part created in 3D-CAD"? Thanks a lot in advance Renee

 January 25, 2014, 23:39 #2 Senior Member   Join Date: Nov 2010 Location: USA Posts: 1,190 Rep Power: 19 A mesh part is a discrete surface - an assembly of triangles that describes some volume. It is not CAD. A 3D-CAD part is a solid CAD geometry built from 3D-CAD. It contains analytic CAD data.

 January 27, 2014, 05:04 #3 New Member   Join Date: Aug 2013 Posts: 14 Rep Power: 8 Do you think there might be a difference for StarCCM+ by using either the leaf-mesh or the CAD part? Do you have an idea where starCCM might have problems? Thanks a lot for your answer.

 January 27, 2014, 11:21 #4 Senior Member   Join Date: Nov 2010 Location: USA Posts: 1,190 Rep Power: 19 Using either datatype shouldn't generate any errors. However they may give different answers. For the mesh part, if the initial mesh is too coarse, then even if you specify smaller sizes for the remeshed surface, you will not get any more detail resolved. A nice analogy to use is a circle. To the computer, a circle is an assembly of lines. As more lines are used, the shape more resembles a circle. A mesh part is a circle with N lines, where N is a constant value. The length of each line is also constant, let's call that X. If you create a remeshed surface that has sizes such that edge lengths smaller than X exist, N does not increase. Therefore although the mesh is finer, the geometry is no more resolved than it was with a smaller mesh. A CAD part is a circle described by an equation (x^2+y^2=r^2). To make a geometry out of it for computation we create a tessellation - a value N. However N is not a constant. We can specify a greater value for N to resolve the CAD as small as we want. Now if our mesh edges fall below X, we can always choose a greater value of N. Furthermore, if we use CAD, we enable features like Project to CAD, where our final mesh has vertices that are projected to the known curve (the equation of the circle, in this case). If that curve does not exist (we don't have CAD), then that feature will not work. Does that make sense?

 February 3, 2014, 06:03 #5 New Member   Join Date: Aug 2013 Posts: 14 Rep Power: 8 Thanks a lot for your reply. It helped, yes

 March 11, 2016, 09:04 #6 New Member   Join Date: Oct 2015 Posts: 1 Rep Power: 0 2 years later, still a useful reply. Thanks.